This invention relates to a combined belt and hydrostatic drive, such as is used to propel a self-propelled agricultural vehicle, such as a combine or the like.
It is known to utilize a variable speed, reversible hydrostatic drive to propel a combine or the like, the hydrostatic drive providing variable speeds within a limited range and being connected to the drive wheels by a conventional multi-speed transmission, so that the combine speed is infinitely variable within the different transmission ranges. Conventionally, the pump in the hydrostatic drive in such a system is connected to the engine by a belt drive system.
With the increasing size and load carrying capacity of modern combines, there has been an attendant increase in the power required to propel the combine, and the increased power requirement has created a problem in providing adequate capacity and durability in the drive belts. In some combines, the variable speed characteristics in the different drive ranges is provided by an infinitely variable belt drive, and it is known to provide a torque sensing mechanism in such a belt drive so that the belt tension is maintained at a lower level when there is a lesser torque demand on the drive system, with the belt tension automatically being increased in response to increased torque demand, so that the high belt tensions that reduce belt life are only applied when necessary. Such a torque sensing variable speed drive is disclosed in U.S. Pat. No. 3,881,370, which is also assigned to the assignee herein. However, to date, there has been no such a torque sensing device for the belt drive in a drive system for a combine or the like that includes a hydrostatic drive.